1. Field of The Invention
The present invention relates to a measurement device for optically measuring interference fringes of a workpiece, especially to a measurement device in which measuring can be performed during machining. The present invention can be preferably applied to measurements while an abrasive working is being performed in lapping, polishing, or another working method. The present invention also relates to a machining device provided with a measurement device.
2. Description of The Related Art
In order to precisely finish a gauge block or the like, machining such as lapping, polishing, or the like is performed using abrasive particles. A machine tool (lapping tool or the like) as a reference and a workpiece are pressed together, and moved relative to each other. Thereby, the workpiece and the working tool slide against each other. Abrasive particles are then introduced between the workpiece and the machine tool. Such systems employing abrasive particles include both liberated abrasive systems and fixed abrasive systems. In a liberated abrasive system, a liquid in which the abrasive particles is suspended is used, and the liquid is supplied between the machine tool and the workpiece. On the other hand, in the fixed abrasive system, the abrasive grains are embedded in a sliding surface of the machine tool. This method of machining is suitable for precisely finishing surfaces, and is commonly applied, for example, to the machining of gauge blocks or other precision components; the finishing of a lens, mirror, or other optical component; or the precise finishing of a semiconductor wafer or the like.
To measure the accuracy of surface or dimension of an abrasively machined workpiece, a measurement device is commonly used to optically detecting interference fringes. Well known examples of such measurement devices, include Fizeau, and Michelson interferometers or the like, and measurement is usually performed using an image of interference fringes generated in accordance with a profile or contour of the workpiece. However, when the workpiece is set on the abrasive machining device, the workpiece is covered with the working tool, and therefore, on-the-fly measurement cannot be performed during working. Accordingly, the workpiece is set on the measurement device and measuring is then performed after the workpiece is detached from the machining device and cleaned.
Generally in lapping or polishing, a micron, submicron, or even higher work accuracy is required. To obtain such a high accuracy, the workpiece is machined again after it has been cleaned and measured. This labor intensive process of working, cleaning, and measuring must be repeated until a required accuracy is obtained. Therefore, the labor cost of highly accurately machined components, especially of optical components or gauges is very high.
Today, there is a strong demand for high density semiconductor elements. To meet the demand, a method is studied in which an in-process semiconductor wafer is flattened through polishing with liberated abrasives and the wafer is patterned again. It has also been proposed that a displacement meter be incorporated in the machining device. In this method, while changes of surface roughness of a workpiece can be measured during machining. The accuracy of flatness or another profile cannot be measured.
As mentioned above, there has been heretofore known no device in which the profile accuracy of a machined surface can be measured on-the-fly during lapping or polishing. Especially, precise measuring cannot be performed through optical detection of interference fringes. Therefore, the profile must be measured by detaching the workpiece being worked from the machining device each time a measurement is necessary, which inhibits improvements to productivity or work accuracy.
In the above, a problem has been described in the example of abrasive working. However, the problem is not limited to abrasive machining. The interference fringes of the machined surface can also not be optically detected during other types of machining.